Hi, When I link my program I get: Build target 'Target 1' linking... *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_MBX_PAGE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_MBX_PAGE_END MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_SEM_PAGE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_SEM_PAGE_END MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_EXTSTKSIZE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_IE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_IEN1 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_IEN2 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_NM_IE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_D_IE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_ND_IE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_NM_IE1 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_D_IE1 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_ND_IE1 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_NM_IE2 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_D_IE2 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_ND_IE2 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_INT_TO_BIT_TABLE_BASE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_MAX_INT_NBR MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_EXTRENTSIZE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_INTSTKSIZE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_TIMESHARING MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_INTREGSIZE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_MAILBOX_SUPPORT MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?RTX_SEMAPHORE_SUPPORT MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL SYMBOL: ?B_CURRENTBANK MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: ?RTX_NM_IE2 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) ADDRESS: 04BAH *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: ?RTX_IEN2 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) ADDRESS: 04BBH *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: ?RTX_NM_IE1 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) ADDRESS: 04BDH *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: ?RTX_IEN1 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) ADDRESS: 04BEH *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: ?RTX_NM_IE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) ADDRESS: 04C0H *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: ?RTX_IE MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) ADDRESS: 04C1H *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: ?RTX_D_IE2 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) ADDRESS: 04CEH *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: ?RTX_IEN2 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) ADDRESS: 04CFH *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: ?RTX_D_IE1 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) ADDRESS: 04D1H *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL SYMBOL: ?RTX_IEN1 MODULE: C:\KEIL\C51\LIB\RTX51.LIB (RTXCREA) ADDRESS: 04D2H Anyone knows the problem ?